The present invention relates to a process for the recovery of high-purity isoquercetin from bioflavanoid mother-liquor residues by extraction of these residues with a solvent mixture comprising methyl acetate and water.
Isoquercetin and also other flavanoids, such as, for example, rutin, have recently been researched intensively owing to their special properties as antioxidants. Free radicals and reactive oxygen compounds play a major role in the human body in respect of ageing and the occurrence of illnesses.
Antioxidants, such as the flavanoids or also vitamin C, are able to scavenge such free radicals and substances and thus reduce their effect on the organism.
Flavanoids, in particular isoquercetin, which also play a major role in combination with vitamin C, are therefore nowadays frequently used and administered as food supplements in pharmaceutical formulations.
The demand for high-purity flavanoids, such as quercetin, rutin or in particular isoquercetin, is therefore increasing. The processes should be inexpensive, and the high-purity products should be obtained in as few reaction steps as possible.
The object was therefore to find an effective process for the recovery of high-purity isoquercetin from the cheapest possible starting material, where the purity of the isoquercetin should preferably be greater than 90% (HPLC).
Surprisingly, it has now been found that high-purity isoquercetin can be recovered from bioflavanoid pastes by extraction of these residues with a solvent mixture comprising methyl acetate and water.
The invention therefore relates to a process for the recovery of isoquercetin from bioflavanoid pastes (mother-liquor residues formed, for example, in the preparation of rutin from Dimorphandra gardneriana), which is characterised in that the following steps are carried out:
a) extraction of the mother-liquor residues (pastes) with a solvent mixture comprising methyl acetate and water in the volume ratio 9:1 in a ten-fold excess, based on the weight of the mother-liquor residues employed, at an extraction temperature of from 35xc2x0 to 50xc2x0 C., and with an extraction time of at least 30 minutes, and separation from the solid raffinate by centrifugation,
b) dilution of the extract with water,
c) removal of the methyl acetate from the extract by distillation under atmospheric pressure,
d) rapid cooling of the aqueous distillation residue to 10xc2x0 C, during which the isoquercetin starts to precipitate,
e) immediate separation and drying of the product.
The bioflavanoid pastes are mother-liquor residues which remain behind in the preparation of pure flavanoids and which usually also contain other flavanoids in relatively large amounts. These residues represent a favourable starting material for the recovery of other flavanoids.
For example, Dimorphandra gardneriana (fava d""anta), contains isoquercetin as a second flavanoid besides rutin, and this inevitably then also arises in the mother liquor during the preparation of rutin. The extraction of mother-liquor residues (pastes) of this type for the recovery of isoquercetin is the subject-matter of this invention.
The isoquercetin is extracted from the mother-liquor residues (xe2x80x98pasta secaxe2x80x99) with a solvent mixture comprising methyl acetate and water in the volume ratio 9:1 in a ten-fold excess, based on the weight of the mother-liquor residues employed, i.e. 10 l of extractant per kg of pasta seca, and separated from the solid raffinate by centrifugation. The raffinate, replenished with fresh pasta seca, can be employed for further extractions.
The raw material here is preferably pre-sieved and introduced slowly into the reactor.
Preference is given to the use of acid-free methyl acetate in order that possible hydrolysis of the isoquercetin is suppressed. The solvent mixture is therefore buffered, for example using a buffer such as ammonium hydrogencarbonate.
The extraction temperature is from 35xc2x0 to 50xc2x0 C. and is thus significantly below the boiling point of methyl acetate (from 55xc2x0 to 57xc2x0 C.). At higher temperature, losses in yield, losses of extractant and filtration difficulties must be expected.
The extraction time is at least 30 minutes. The extraction is preferably carried out for from 30 to 60 minutes. Although a longer extraction time of up to 6 hours does not cause any damage, it only improves the purity to an insignificant extent.
The extract is diluted with water (demineralised water), preferably 60-80% by volume, particularly preferably 60-70% by volume, of the amount of extract, and the methyl acetate is distilled off under atmospheric pressure. A bottom temperature of at most 70xc2x0 C. is preferably selected here.
The extract should wherever possible be further processed immediately within 1 hour, since otherwise reductions in purity due to uncontrolled crystallisation may occur.
The addition of the amount of water may optionally also be carried out in portions and delayed until during the distillation.
The distillate still contains about 5% by weight of water (by the Karl Fischer method) and can be re-used after adjustment of the water content. About 85% by weight of the methyl acetate employed can be recovered in this way.
The aqueous distillation residue is cooled rapidly to 10xc2x0 C., preferably within a maximum of 2 hours, during which the isoquercetin begins to precipitate.
About 80% of the total amount of isoquercetin precipitating precipitates in very finely crystalline form with high purity directly during the cooling. An HPLC check shows that the product consists of 94% of isoquercetin, 1% of rutin and 0.2% of quercetin. The preferred aim of recovering isoquercetin in a purity of greater than 90% is thus achieved.
The product must be separated off immediately, since on further stirring the crystal structure becomes coarser and the content drops since essentially only quercetin precipitates.
The product is then dried, which is preferably carried out in a vacuum drying cabinet at from about 80 to 120 mbar and a drying temperature of at most 45xc2x0 C.
Should it be impossible to process the extract further immediately or should the precipitated product have stood for too long by mistake, a reduction in purity can be expected. However, the purity of the desired isoquercetin can be further improved by further purification steps.
A possible further purification step that may be mentioned is, for example, removal of quercetin impurities by stirring with methyl tert-butyl ether.
Another possibility for further purification is brief boiling with water followed by filtration.
For performance on a larger scale, the process according to the invention can also be carried out semi-continuously. The semi-continuous process is also a subject-matter of this invention.
The procedure here is to pass the requisite amount of solvent (where the solvent mixture is likewise composed of methyl acetate and water in the volume ratio 9:1) through an extractor with filter plate which contains a highly concentrated suspension of mother-liquor residues.
The extractor volume and volume flow rates are set in such a way that a residence time in the extractor of at least 30 minutes is maintained. After a run-in phase from one residence time during which the extractor is operated in circulation, fresh, temperature-controlled solvent mixture is passed into the extractor and at the same time the same amount of extract is withdrawn, so that the working volume in the extractor remains constant. The temperature in the extractor here is selected between 35xc2x0 and 50xc2x0 C.
The withdrawn extract is immediately concentrated to give the aqueous residue, it being possible for the distillate (water content 4.2%) to be reused directly for the extraction after water adjustment.
If the further steps of crystallisation, where appropriate also the purification by boiling with water and stirring with methyl tert-butyl ether are carried out in the same apparatus after discharge of the extraction residue, the continuously solid product phase remains in the apparatus for the entire time, and consequently some filtration steps are superfluous, thus minimising product and operating-material losses.
During purification of the crude isoquercetin, purification by boiling with water may also be preferred to removal of quercetin using MTBE""ether, since it may also be possible to remove some of the quercetin with the aqueous mother liquor.